Backpack cooler



FIG. 1 is a perspective view of a backpack cooler showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a right side elevational view thereof;

FIG. 4 is a front elevational view thereof;

FIG. 5 is a rear elevational view thereof; and

FIG. 6 is a bottom plan view thereof. 

The ornamental design for backpack cooler, as shown and described. 